Molecular Dynamics Simulation On Framework Structure Of Coal Dense Medium Component Under Heating Treatment

Coal dense medium component?DMC?from the coal all-components group separation served as the material.After fractional and multiple extract of DMC with n-hexane,methanol,acetone and chloroform,DMC framework molecules were obtained.Through ¹³C CP/MAS NMR analysis,the related information of the framework structure of the dense medium component was obtained.On this basis,the molecular model of the framework structure of the dense medium component was constructed and optimized.Based on the molecular dynamics simulation software-Materials Studio,the evolution process and energy parameter changes of the dense medium component framework molecules under thermal action were studied,and the mesophase spherule formation mechanism was explored at the molecular level based on the experimental results of mesophase spherule formation.The aromaticity of dense medium component framework structure is 64%,aliphatic carbon content is 22.8%,aliphatic hydrogen and aromatic hydrogen ratio is2.28,and the X_BPP is 0.23.Aromatic unit mainly for 2-3 ring-condensed polycyclic aromatic and the subsidiary role of four-ring.After the minimum energy optimization,the density was 1.12 g/cm³,which was very close to the dense medium component framework density determined by the experiment.With the increase of temperature,the specific volume of dense medium component framework molecular system showed a stepped-type rising trend.The first step is caused by local layered structure formed by local parallel superposition of framework molecules.The second step is caused by the formation of local lamellar structure molecules that further intersect and fuse with each other to form multi-point multi-region lamellar stack.The simulation results can better explain the process of mesophase spherule formation and growth from the dense medium component under thermal action.At360°C,by generating local parallel superposition,the framework molecules form local layered structure,and then form mesophase spherical nanoparticles.360-430°C,stable framework molecules continue to generate small mesophase sphere nanoparticles.430-450°C,further cross fusion have been generated,nanoparticles to form more multipoint multizone layered stacked structure,so that the mesophase spherical nanoparticles grew up into a particle,the bright light points can be observed under polarized light microscope.450-530°C,mesophase spherical particles continue to cross and grow up,more local layered stack structure more widely and more abundant.The bright spot is more obvious under polarizing microscope.After 530°C,the mesophase spherule melts and merges into the body mesophase,and finally forms the wide-area streamlined mesophase.